Endeavour saw the damage Touya's quirk did to his body and immediately put a stop to their training, even though it seems like something Touya really enjoyed doing with his father. However, the seed of wanting to surpass All Might had already been rooted in Touya's mind.

The more Endeavour pulled away in an attempt to get his son to stop wanting to become a hero like him and damaging his body, the harder Touya trained to get his father's approval. Touya didn't see it as protection - he saw it as rejection.

Even though they were happy w/ just Touya and Fuyumi, this suggests Enji and Rei decided to try for more kids until they made the perfect one to show Touya he couldn't be the perfect child for his dad's goal. Also 'cause of Endeavour's growing fixation on making the perfect quirk

Despite having made Shouto, a perfect combination of their quirks, it's shown that Endeavour genuinely still cared for Touya and his safety since he basically begs him to stop using his quirk and develop a life outside of it as the damage it does to his body becomes more drastic.

With Touya, Endeavour tried to dissuade him from using his quirk at all, however it's very difficult to separate a child from the thing he believes gives him worth, especially in a hero centric society. The way they handled Touya ended up destroying him.